Preeclampsia (PE) adversely affects as many as 20% of pregnancies in the USA. One of the earliest events is the failure of maternal vascular endothelium vasodilatory function to adapt, with the normal pregnancy-associated increase in NO being blunted or lost. In our previous funding period we used dual imaging of [Ca2+]i and NO in freshly isolated uterine artery endothelium to show that in normal pregnancy, enhancement of Ca2+ signaling is the primary cause of enhanced NO production, and such enhancement depends on specific changes in function of Ca2+ signaling mediators. Sustained Ca2+ entry into UA endothelium occurs through TRPC channels but our preliminary data also suggests the pregnancy enhanced opening of TRPC channels in turn depends on CX43 Gap junction communication, and that such coupling of cells may occur at an electrical level. Our data further suggests membrane hyperpolarization by KCa type channels connects increased Gap junction function to enhance TRPC function in pregnancy. Consistent with this, UAEC show sensitivity to antagonists of KCa function (Apamin and Tram34) with a resulting reduction in Ca2+ signaling. If this model is correct then future therapy for failed adaptation of Ca2+ signaling in PE pregnancy could be achieved by the use of SK or IK type KCa channel agonists. In this renewal we propose to test this model, moving from isolated cells in culture to whole vessels ex vivo to whole animal studies. We will examine 1) Changes in membrane potential and KCa current activity in response to ATP in NP- and P-UAEC in cells at low vs high density, dependence of these changes on gap junction function, and determine the effect of antagonists Apamin and Tram-34 or the selective agonist NS309 on Ca2+ burst activity to implicate KCa channels in this response; 2) Examine the effects of these same antagonists and agonists on changes in Ca2+, membrane potential and NO production in intact UA vessels ex vivo; 3) determine if the KCa agonist NS309 is comparable to the effects of ATP/UTP in mediating NO dependent increases in blood flow in uterine artery in vivo during pregnancy, and also the extent to which SK and/or IK types of KCa channel mediate this effect. In this way we take our recent advances in mechanistic knowledge of pregnancy adaptation of blood flow to now establish the validity of using KCa channel agonists to maximize this response in vivo in pregnancy and particularly those complicated by PE. Success could have major impact on strategies to improve treatment of human PE pregnancy where this otherwise normal adaptive response has failed and is resistant to current therapies.